1. Field of the Invention
This invention relates to tracking systems, more particularly, tracking systems for determining the location of components, assemblies, and sub-assemblies in medical instruments.
2. Discussion of the Art
Radio frequency identification (RFID) technology is an identification technology, which is capable of being automated, in which data are written to and data are read from tags that contain a microchip and an antenna by means of radio frequency signals. Radio frequency identification technology allows an active transmitter to selectively interrogate radio frequency identification tags attached to items of interest and capture the data transmitted from these radio frequency identification tags.
There are several methods for storing identification information in radio frequency identification systems, but the most common method involves storing a serial number that identifies a person or object, and other information, if desired, on a microchip, which is attached to an antenna. The microchip and the antenna together are referred to as a radio frequency identification transponder or a radio frequency identification tag. The antenna enables the microchip to transmit the identification information to a reader. The reader converts the radio waves transmitted from the radio frequency identification tag into digital information that can then be further transmitted to computers, which can use the information for various purposes.
Radio frequency identification tags can be provided in various shapes and sizes, can respond to various frequencies, and can be of various types. The shape(s) and the size(s) of a radio frequency identification tag(s) are generally a function of the radio frequency selected and the desired range, i.e., the distance between the radio frequency identification tag and the transmitter.
Radio waves behave differently at different frequencies; consequently, the appropriate frequency for a radio frequency identification tag must be selected for a given application. The available area of an object upon which the radio frequency identification tag can be attached or affixed is another factor that must be accounted for in the balancing of parameters necessary to determine a configuration. Frequencies for radio frequency identification tag are classified into three main categories: low frequency, around 125 KHz, high frequency, around 13.56 MHz, and ultra-high frequency, or UHF, around 860-960 MHz. Microwave frequency, around 2.45 GHz, can also be used in some applications. Radio frequency identification tags that utilize low frequency radio waves use less power, and, consequently, are more suitable for use for penetrating non-metallic substances than are radio frequency identification tags that utilize ultra-high frequency radio waves. Radio frequency identification tags that utilize low frequency radio waves are preferred for scanning objects having a high content of water, such as fruit, but their reading range is limited to less than a foot (0.33 meter). Radio frequency identification tags that utilize high frequency radio waves are useful for objects made of metal, and they can function well in the vicinity of objects having a high content of water. Radio frequency identification tags that utilize high frequency radio waves have a maximum reading range of about three feet (1 meter). Radio frequency identification tags that utilize ultra-high frequency radio waves typically provide greater range and can transfer data faster than can radio frequency identification tags that utilize low frequency radio waves or radio frequency identification tags that utilize high frequency radio waves. However, radio frequency identification tags that utilize ultra-high frequency radio waves require more power than do radio frequency identification tags that utilize low frequency radio waves and are less likely to pass through materials such as liquids and metals. Therefore, radio frequency identification tags that utilize ultra-high frequency radio waves generally require a clear path between the radio frequency identification tag and the reader. Radio frequency identification tags that utilize ultra-high frequency radio waves may be more useful for scanning labels on boxes of goods as they pass through a dock door into a warehouse than they would be for reading radio frequency identification tags that require a shorter read distance and a slower speed for reading, such as, for example, radio frequency identification tags that are used for controlled access to a building.
There are three types of radio frequency identification tags: passive, active, and semi-passive. Passive radio frequency identification tags are battery-free data-carrying devices that react to a specific reader produced inductively coupled or radiated electromagnetic field, by delivering a data modulated radio frequency response. Passive radio frequency identification tags draw power from the reader, which emits electromagnetic waves that induce a current in the antenna of the radio frequency identification tag. Active radio frequency identification tags are radio frequency identification tags that have a transmitter to send back information, rather than reflecting back a signal from the reader, as the passive radio frequency identification tag does. Active radio frequency identification tags have their own power source (typically a long-life battery). The power source is used to provide power to the circuitry of the microchip and to broadcast a signal to a reader. Such activity is analogous to the manner in which a cellular telephone transmits signals to a base station. Semi-passive radio frequency identification tags are radio frequency identification tags having batteries, but they communicate using the same backscatter technique as do passive radio frequency identification tags. They use the battery to provide power to run the circuitry of a microchip and sometimes an onboard sensor. They have a longer read range than a regular passive radio frequency identification tag because all of the energy gathered from the reader can be reflected back to the reader. Active and semi-passive radio frequency identification tags are useful for tracking goods of high value that need to be scanned over long ranges, such as railway cars on a track. However, active and semi-passive radio frequency identification tags are more expensive than are passive radio frequency identification tags, thereby making their cost too expensive for objects having a low value. However, future developments are expected to bring about a reduction in the cost of active radio frequency identification tags. Users often prefer passive radio frequency identification tags that utilize ultra-high frequency radio waves, which cost less than 40 U.S. cents per tag when ordered in volumes of one million tags or more. The range for reading passive frequency radio frequency identification tags that utilize ultra-high frequency radio waves is not as great as that of active radio frequency identification tags, e.g., less than 20 feet as compared with 100 feet or more for active radio frequency identification tags, but they are far less expensive than are active radio frequency identification tags and can be disposed of with the packaging for the object.
Most manufacturers of radio frequency identification tags do not quote prices, because pricing is based on volume, the memory capacity of the radio frequency identification tag, and the packaging of the radio frequency identification tag, e.g., whether the radio frequency identification tag is encased in plastic or embedded in a label. A typical cost for a 96-bit Electronic Product Code radio frequency identification tag ranges from about 20 to about 40 U.S. cents. If the radio frequency identification tag is embedded in a thermally transferred label onto which a bar code can be imprinted, the price rises to 40 U.S. cents, and even higher. The cost of a low frequency transponder encapsulated in glass is about $3.50, and the cost of a low frequency transponder in a plastic card or key fob is about $4.00 and can often be higher. The cost of high frequency transponders ranges from about $2.50 (in a card) to about $6.00 or more (for a key fob or other special embodiment).
The Department of Defense has employed radio frequency identification technology since the early 1990s to manage its complex supply chains around the world. There have been numerous developments in the capability of the technology to support this effort and further developments are expected as global standards in transmitter/receiver technology and data synchronization gain widespread acceptance. Transmitter and receiver frequency standards ensure that radio frequency identification tags and readers can operate in any electronic environment around the world. The International Organization for Standardization (ISO) is developing standards for tracking goods in a supply chain by means of high frequency radio frequency identification tags (ISO 18000-3) and ultra-high frequency tags (ISO 18000-6).
The Electronic Product Code (EPC) is a family of coding schemes that were created as the eventual successor to the bar code. The EPC was created as a low-cost method for tracking goods by means of radio frequency identification technology. The EPC is a serial, created by the Auto-ID Center, which will complement bar codes. The EPC has digits to identify the manufacturer, product category, and the individual item. The EPC system is currently managed by EPCglobal, which is a joint venture between GS1 and GS1 US. EPCglobal is an organization set up to achieve world-wide adoption and standardization of the Electronic Product Code technology in an ethical and responsible way. EPCglobal has its own standardization process, which was used to create bar code standards. EPCglobal intends to submit EPC protocols to ISO so that these protocols can become international standards. The following table (TABLE 1) lists radio frequency identification tag categories as defined by standards established by EPCglobal:
TABLE 1ParameterClass 0Class 1Class 1 Generation 2FrequencyAllAllAllRead RateU.S.: 800 tags/secondU.S.: 200 tags/secondU.S.: 1700 tags/secondEU: 200 tags/secondEU: 50 tags/secondEU: 600 tags/secondRewriteabilityRead OnlyWrite OnceFully RewritablePrivacy24-bit password8-bit password32-bit password(ConcealedMode)SecurityReader broadcasts theReader broadcasts theReader does notidentification numberidentification numbertransmit the identificationof the radio frequencyof the radio frequencynumber of the radioidentification tag, i.e.,identification tag, i.e.,frequency identificationthe signal can bethe signal can betag. Authenticationreceived by anyone.received by anyone.Encryption is required,i.e., confidentialauthorization must beused to obtain access toinformation.RegulatoryNorth AmericaNorth AmericaWorld-wideComplianceMulti-ReaderTransmissions fromTransmissions fromReader transmissionsEnvironmentthe reader arethe reader interfere,are separated, i.e.,separated physically,but the reader usersreader guard bandsi.e., a physicalalgorithm(s) to selectprevent collisions. Thisseparation reducesthe appropriate signal.protocol is ansignal crossover andenhancement of theinterference.protocol of the Class 1radio frequencyidentification tag.
The major differences between the Class 0 and the Class 1 radio frequency identification tags are twofold. The first is that the Class 0 radio frequency identification tag has been defined by EPCglobal as a read-only device. A number is placed on a radio frequency identification tag, the number can be read, but it cannot be modified. The Class 1 radio frequency identification tag has been defined in the EPCglobal specification as a radio frequency identification tag that is one-time programmable. In other words, the radio frequency identification tag starts off as blank, the EPC is encoded, and that code can never be changed again. In practice, the originator of the Class 1 radio frequency identification tag now has radio frequency identification tags that are re-programmable, and the originator of the Class 0 radio frequency identification tag has a radio frequency identification tag that is fully re-writeable. However, the Class 0 radio frequency identification tags and the Class 1 radio frequency identification tags did not provide the data functionality nor did they meet geographic RF emission requirements across the world. Accordingly, the Class 1 Generation 2 radio frequency identification tags will be designed to support the 96-bit EPC code and have the provision for extra data to be carried in the radio frequency identification tag based on a single radio frequency identification protocol. Although the Class 0, the Class 1, and the Class 1 Generation 2 radio frequency identification tags are now available, it is expected that radio frequency identification tags that use high frequency radio waves and that are in compliance with the Class 1 Generation 2 radio frequency identification tags will become the dominant type of radio frequency identification tag on packaging. There is still support in the standards for the Class 0 and the Class 1 radio frequency identification tags, which support is likely to continue into the future so long as these radio frequency identification tags continue to constitute a large proportion of the technology in use. It should also be noted that at least four other classes of radio frequency identification tags exist, namely, Class 2, Class 3, Class 4, and Class 5 radio frequency identification tags, which are described in CHAUDHRY, N., THOMPSON, D., and THOMPSON, C., RFID Technical Tutorial and Threat Modeling Version 1.0 [online], Dec. 8, 2005 [retrieved on Jun. 9, 2008]. Retrieved from the Internet: <URL: http://www.csce.uark.edu/˜drt/presentations/rfid-tutorial-threats-051201.pdf>, incorporated herein by reference.
Radio frequency identification technology has been contemplated for improving the configuration control of medical instruments and the supply chain visibility of components, assemblies, and sub-assemblies of medical instruments. Currently, information relating to the identity of the components, the assemblies, and the sub-assemblies of medical instruments and the maintenance and replacement of these components, assemblies, and sub-assemblies are recorded manually, and the repairs and replacements are recorded in writing. This procedure can lead to transcription errors and missing or inaccurate information. The manually recorded information is not readily accessible or traceable, and is not in a form that can be communicated to those who need to know the status regarding the configurations of the numerous medical instruments in assorted locations over a wide geographical area.